| China has proposed to establish a scientific research base on the Moon in the future to carry out deeper exploration of the Moon.The unmanned lunar rover,as an essential and important vehicle for the lunar exploration mission,will also be used in a large number of deeper exploration of the Moon in the future.However,the soft lunar soil on the lunar surface will often cause the rover to slip,sink or even fail,so the lunar wheels,as the core walking parts of the rover,are directly related to the success or failure of lunar exploration missions.In the future,the unmanned lunar rover will face harsher and more variable working environment,more complex working conditions,larger exploration range and faster moving speed requirements when deeper exploration of the Moon is carried out.Therefore,the unmanned lunar wheels will be required to have better traction performance,more reliable passing performance and lower power loss in the future.The preferred structural form of the unmanned lunar wheel is the screen wheel,but it is already difficult to improve the traction throughput performance of the unmanned lunar screen wheel through conventional optimization design to meet the more demanding mission requirements in the future.The ostrich(Struthio camelus)has acquired the special ability to run at high speed in a sandy environment without slipping during its long-term evolution,mainly due to its special foot and toe structure.Therefore,in this study,in order to seek a better design of unmanned screen wheel,an unmanned lunar exploration screen wheel with ostrich foot and toe characteristics was designed by applying engineering bionics principles with ostrich foot and toe as the bionic prototype.First,Summarizing the research results of our group,we have sorted out the mechanism of the sand fixing and flow limiting effect of the ostrich plantar surface and the gripping effect of the ostrich toenail.The"concave and convex"characteristics of the ostrich plantar surface and the toe nail configuration are refined and simplified,and from the perspective of the practical engineering application of the lunar screen wheel,they are incorporated into the screen wheel,and an unmanned lunar screen wheel with ostrich foot and toe characteristics is designed.A comparison wheel was also designed as a control test.Then,The intrinsic parameters of the simulated lunar soil used in this study were measured,and the density,water content,and elastic modulus were 1.45 kg/m~3,0.82%,and 24 MPa,respectively.The four typical shapes are summarized and summarized as wedge,polygon,elongated and spherical.The four particle models are established in EDEM according to the four typical shapes.The particle size parameters of the simulated lunar soil were determined,and the particle size distribution of the discrete element simulation was calibrated.The stacking angle of the simulated lunar soil was determined to be 37.8~°,and the interaction parameters were calibrated and verified to be 0.483 for the static friction coefficient,0.086 for the rolling friction coefficient,and0.439 for the recovery coefficient,respectively.Then,The simulation environment was established using the calibrated discrete element parameters.Discrete element simulation tests were conducted on the bionic wheel and the comparison wheel,and the following conclusions were obtained:the maximum traction force of the bionic wheel was about 35%-40%higher than that of the comparison wheel under the test conditions,and the traction force of the bionic wheel was always higher than that of the comparison wheel,indicating that the traction capacity of the bionic wheel was better than that of the comparison wheel as a whole;the maximum sinkage of the bionic wheel was 16%-30%higher than that of the comparison wheel under the test conditions;the traction efficiency of the bionic wheel was always higher than that of the comparison wheel at low slip rate under the test conditions,and the maximum traction efficiency of the bionic wheel was about 28%higher than that of the comparison wheel.Under the test conditions,the traction efficiency of the bionic wheel is always higher than that of the comparison wheel at low slip rate,and the highest traction efficiency of the bionic wheel is about 28%higher than that of the comparison wheel,indicating that the traction efficiency of the bionic wheel is higher and more energy-efficient at low slip rate;under the test conditions,the median value of the driving torque of the bionic wheel is about 15%higher than that of the comparison wheel,indicating that the driving torque of the bionic wheel is higher than that of the comparison wheel under the same test conditions;comparing the wheel ruts of the two wheels,it is found that It is found that the rutting of both the bionic wheel and the comparison wheel gradually deteriorates with the increase of slip rate.The bionic wheel spurs can provide counteraction thrust to the wheel directly;the force between the bionic wheel spurs and the particles is more regularly distributed compared with the ordinary rectangular wheel spurs,which can concentrate the particle force as thrust,indicating that the bionic wheel spurs can improve the traction performance of the bionic wheel.This proves that the design of the bionic wheel surface and bionic wheel spurs is successful and can achieve the desired engineering bionic function.In summary,the simulation tests show that the traction performance of the bionic wheel is better than that of the comparison wheel,and the traction efficiency of the bionic wheel is higher and more energy-efficient at low slip rate,which indicates that its design scheme is feasible.Finally,the wheel prototype was machined and assembled,and the traction through performance test test was conducted.The following conclusions were obtained:under the test conditions,the maximum traction force of the bionic wheel was increased by about 30%-40%compared with that of the comparison wheel,indicating that the traction performance of the bionic was better than that of the comparison wheel.It was also found that the curved wheel surface of the ostrich foot played a major role in improving the traction performance,and the toenail wheel spur of the ostrich played a minor role;under the test conditions,the traction efficiency of the bionic wheel was higher than that of the comparison wheel at low slip rate,and the peak traction efficiency of the bionic wheel increased by about 25%-34%compared with that of the comparison wheel,indicating that the bionic wheel had higher and more energy-saving traction efficiency at low slip rate.Under the test conditions,the maximum sinkage of the bionic wheel is about 31%-50%higher than that of the comparison wheel.Under the test conditions,the driving torque of the bionic wheel during wheel travel is about7%-14%higher than that of the comparison wheel during travel as a whole,indicating that the driving torque required by the bionic wheel is greater under the same condition;it is found that the degree of rutting destruction of the bionic wheel and the comparison wheel increases with the increase of slip rate by analyzing the rutting morphology.At the same time,it is found that the bionic wheel surface can play the role of fixing the simulated lunar soil,thus improving the traction passing ability.In summary,it can be concluded that the traction-passing performance of the bionic wheel is better than that of the comparison wheel and more energy-efficient,and this study has an important reference value for the research of lunar exploration screen wheels. |
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